I hate to be a fence-sitter…..but it depends. Both exercises are excellent to challenge core ab muscles. If you have a client with weak shoulder girdle stability or weak wrists – go for the forearms as the full plank could be considered more “challenging” for the shoulders and wrists and they’ll still get the benefit of the abs.
I get asked this alot too! (… and I like the word “challenging” rather than “difficult” myself)
Performing the plank on hands or forearms all depends on which area you are targeting and your physical capabilities. When the plank is performed on the hands the triceps and shoulder muscles are more activated while the body is positioned more vertically against gravity . So when a plank is performed on the hands, you’ll feel your shoulders and triceps more and your core less.
If your goal is to develop shoulder strength and stabilization then the elevated plank on hands is probably more appropriate. You might also find relief from wrist pain in doing the plank this way by holding in to hex dumbbells pointing toward the front edge which will allow the wrists to be in a more neutral position or use a wedge/pad to lift the heel of the hand enough to relieve pressure on the joint.
If the plank is done from the forearms the triceps work less and although this version open’s up the shoulder joint, the core is working much more due to the shift in center of gravity so if your goal is core strength then you should choose the lower forearm position
They are both equally as difficult, however, it is more of a personal preference I think. To kick it up a notch I suggest doing what I call Plank Up & Downs. Begin in the plank position, raise your body upwards with your left arm, then your right, then left arm down, and followed by the right arm. Start with your left arm, then at 30 seconds switch to the right. Get ready to sweat! And pant lol 🙂
I just like to throw in one comment about the question of shoulder stabilization which some fellow trainers have already alluded to.
I often observe that – in the interest of strengthening ‘the core’ – the issue of shoulder girdle integrity is completely ignored. Even in a position on all fours, I often see shoulders that look truly ‘unhinged’ with the head hanging down and the shoulder blades sticking up. I would suggest that this person does not need to do a plank either way until the shoulder have greater strength to deal with such a load.